In a rechargeable secondary battery field, an aqueous solution based battery such as a lead battery, a nickel cadmium battery or a nickel hydrogen battery has been mainly used. However, as an electric apparatus is downsized and reduced in weight, attention has been given to a lithium ion secondary battery with a high energy density, and research, development and commercialization of the lithium ion secondary battery is rapidly proceeded.
Further, in a view of global warming or depletion of fuel resources, an electric vehicle (EV) or a hybrid electric vehicle (HEV) in which an electric motor assists a part of driving is developed by vehicle manufacturers, and a high-capacity and high-voltage secondary battery is required as a power source of the vehicle. As a power source which meets the requirement, a nonaqueous solution battery with high voltage is focused on. Especially, since a packed rectangular lithium ion secondary battery has an advantage of good volumetric efficiency, expectations for a development of the rectangular lithium ion secondary battery for the HEV or the EV have been increased.
In large current application for the HEV or the EV, heat generation of the battery is unavoidable, and to cool the battery is necessary. Generally, in an assembled cell in which a plurality of batteries electrically connected in series or in parallel, gap is provided between each battery, and the battery is cooled by flowing coolant such as air into the gap. Further, in each battery forming the assembled cell, a battery container may be expanded when an electrode material housed in the battery container is expanded due to charging.
As an assembled cell which is capable of reducing the expansion of the battery container, a secondary battery assembly in which secondary batteries are bound in a state in which a side surface having a maximum area (pressed surface) of outer surfaces of the secondary battery is partially compressed is disclosed (see Patent Literature 1 below).
The secondary battery assembly described in Patent Literature 1 has a purpose, in a secondary battery which is used in a high rate in which the battery is repeatedly charged and discharged with a large current, to reduce a performance degradation of the secondary battery by holding the secondary batteries to keep uniform face pressure on the pressed surface, thus the secondary battery assembly has a contact member and a binding member as a solution means. The contact member has a plurality contact parts which is arranged discretely, each of which contacts with the pressed surface. The contact parts are formed to protrude from a connecting part toward the pressed surface, and the contact parts are arranged or formed to press less strongly a central region of the pressed surface between both one-side regions, the central region corresponding to a part close to the center of a wound electrode body in a winding axis direction. Specifically, to provide the contact member such that top of the contact member which contacts the pressed surface is curved to be concave at the center and pressing force to the pressed surface is different according to parts of the surface is described. On the other hand, to determine an arrangement of each member such that the contact member does not contact with an end part of a cell case in order not to press the end part of the cell case is described.